Did you know the first metal detector was invented by Alexander Graham Bell in 1881 in order to extract a stray bullet from President James Garfield's back? This is the kind of interesting innovation revealed in IBM Think, a free app that maps out the roots of technological advances.

What does it do?

With a 10-minute HD video and interactive illustrations, it shows the origins of a lot of the technology we use today.

Why do we like it?

Science has come a long since Galileo first made his claims of a sun-centric universe, but that doesn't mean the earliest advances are any less important. In fact, early revelations such as those laid the foundation for what has come since—space exploration, complicated computing, and so forth. And that is important to recognize, as IBM explains so beautifully. This masterfully designed app explores the most crucial leaps of progress, and how they've made our world a better place. Based off of IBM's Think exhibit, which was staged last year in New York City, the app is the kind of mind-expanding tool that is interesting, as well as understandable, to kids and adults.